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A process requesting a system task to be executed in the context of
another process will be notified by a message when the task has
executed. This message will be on the form:
{RequestType, RequestId, Pid, Result}.
A process requesting a system task to be executed can set priority
on the system task. The requester typically set the same priority
on the task as its own process priority, and by this avoiding
priority inversion. A request for execution of a system task is
made by calling the statically linked in NIF
erts_internal:request_system_task(Pid, Prio, Request). This is an
undocumented ERTS internal function that should remain so. It
should *only* be called from BIF implementations.
Currently defined system tasks are:
* garbage_collect
* check_process_code
Further system tasks can and will be implemented in the future.
The erlang:garbage_collect/[1,2] and erlang:check_process_code/[2,3]
BIFs are now implemented using system tasks. Both the
'garbage_collect' and the 'check_process_code' operations perform
or may perform garbage_collections. By doing these via the
system task functionality all garbage collect operations in the
system will be performed solely in the context of the process
being garbage collected. This makes it possible to later implement
functionality for disabling garbage collection of a process over
context switches.
Newly introduced BIFs:
* erlang:garbage_collect/2 - The new second argument is an option
list. Introduced option:
* {async, RequestId} - making it possible for users to issue
asynchronous garbage collect requests.
* erlang:check_process_code/3 - The new third argument is an
option list. Introduced options:
* {async, RequestId} - making it possible for users to issue
asynchronous check process code requests.
* {allow_gc, boolean()} - making it possible to issue requests
that aren't allowed to garbage collect (operation will abort
if gc should be needed).
These options have been introduced as a preparation for
parallelization of check_process_code operations when the
code_server is about to purge a module.
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